In many industries, sheets and webs of indeterminate length are fed to various processing apparatus, such as printing, gluing, winding, etc. It is important in many instances that these sheets and webs be cleaned of dust and particles.
A known sheet and web cleaning apparatus is disclosed in U.S. Pat. No. 5,596,783 to Testone, a copy of which is incorporated herein by reference in its entirety. In the Testone '783 patent a sheet or web cleaner comprises a pair of substantially identical facing units, each having a longitudinal suction hood having a generally rectangular inlet slot therein. On either side of and parallel to the inlet slot is a channel containing a pressurized ionizing bar which comprises a hollow tube, a plurality of ionizing points extend from the tube, and small holes adjacent each ionizing point discharge air at high velocity. The sheet or web passes through a pair of opposed units transversely of the longitudinally extending suction hoods, and between respective faceplates on the units.
Each faceplate is of a smooth, hard material, such as aluminum, steel or a hard plastic material, and has in a face side facing toward the sheet or web a series of spaced, parallel ridges which extend part way through a thickness of the faceplate. The ridges are aligned parallel to each other and are inclined relative to the direction of movement of a sheet or web through the apparatus, and are also inclined to the axis of the suction hood, and to the axes of the ionizing bars. The parallel aligned ridges each have a leading end and a trailing end relative to the direction of travel of the sheet or web, and are aligned obliquely with respect to the direction of travel. In one longitudinal portion of each faceplate the leading ends of the ridges are substantially oriented so as to point away from a co-planar transverse center line through the faceplate in the direction of travel of the web, while the trailing ends are substantially oriented so as to point towards the transverse center line. In another longitudinal portion of each faceplate the leading ends of the ridges are substantially oriented so as to point toward the transverse center line while the trailing ends are substantially oriented so as to point away from the transverse center line.
The ridges of the faceplate are of generally triangular cross-section, each having an apex facing towards and relatively close to the sheet or web, and facing away from the suction hood. Spaces between the ridges provide a plurality of converging air paths which are in communication with elongate openings in an oppositely facing face side surface of the faceplate, and which extend partly through the faceplate thickness.
In the oppositely facing face side surface of the faceplate there is a central, elongate inlet opening of tapering width, with the greater width remote from a suction end of the suction hood in order to permit substantially equal volumes of air to flow into the suction hood through its rectangular inlet slot irrespective of a relative position along a longitudinally extending length of the suction hood. There is also an elongate side discharge opening in the faceplate on either side of the central tapered inlet opening, each of which is in registry with a corresponding ionizing bar to permit ionized air discharged from the ionizing bars to flow through the respective discharge openings in the faceplate and through the spaces between the ridges.
High velocity ionized air currents created by the flow of ionized air from the ionizing bars flows through the respective discharge openings in the faceplate and through the spaces between the ridges. The high velocity ionized air strikes the moving sheet or web neutralizing the static electricity on both the sheet or web material being processed and the contaminant particles dislodging the particulate making the particulate airborne, while an airflow induced by suction draws the air and airborne particles into the suction hood.
The above described prior art apparatus has been found to have a deficiency when cleaning relatively lightweight, sensitive web materials such as tissue papers, thin gauge films and/or metal foils. In applications involving thin, lightweight sheets or webs the lightweight sheets or webs have been found to be susceptible to a lateral displacement by the induced air current relative to the direction of travel of the web. When the high velocity air strikes the lightweight sheet or web, the sheet or web material on the one longitudinal side of the apparatus whose leading ends of the ridges are oriented so as to point away from the transverse centerline have been found to track along and follow the path of the ridges from their respective leading ends toward the trailing ends as the sheet or web travels along the direction of travel. The result has been that a lateral side portion of the sheet or web on the one longitudinal side tended to be displaced towards the transverse centerline as the web traveled through the apparatus with the result that the sheet or web material became bunched up and wrinkled along the one longitudinal side. Consequently, the one longitudinal side could not be adequately cleaned, and downstream processes were adversely impacted because the sheet or web was not smooth and wrinkle free. This required that the entire sheet or web feeding and handling apparatus be stopped, and that the web material be straightened and smoothed out. This was time consuming, required labor to remedy the situation, and caused interruption of production.
It has been further observed that lightweight sheets and webs tend to travel through the cleaning apparatus tangential to the face side of one or the other of the faceplates of the opposed units; and that due to transient variations in, for example, the suction or an amount of tension under which the sheet or web is drawn through the apparatus, the faceplate against which the sheet or web travels tangentially can change, the sheet or web sometimes exhibiting oscillatory behavior wherein the sheet or web flutters between the opposed faceplates.
Due to the inconsistent and sometimes oscillatory behavior of the sheet or web relative to the faceplate against which the sheet or web aligns itself tangentially, attempts to mitigate the lateral displacement of the sheet or web by using two similarly structured, oppositely aligned faceplates, a first faceplate with a general left-to-right alignment of the ridges, and a second faceplate, identical to the first, but installed in an inverted or opposed orientation relative to the first faceplate and thus having a general right-to-left alignment of the ridges have been unsuccessful.